JPS6341993B2 - - Google Patents

Description

[Detailed description of the invention]

BACKGROUND OF THE INVENTION The present invention relates to apparatus and methods for purifying gases, and more particularly to apparatus and methods for purifying hydrogen gas. Many of today's industries are
Use hydrogen with a purity of 99% or higher. Chemical manufacturers, food manufacturers, and electronics manufacturers, to name a few, require pure hydrogen for a variety of purposes. Most industrial methods for producing hydrogen are
Provides hydrogen at concentrations lower than 75%. Catalytic steam reforming of natural gas or light hydrocarbons, partial oxidation of heavy hydrocarbon feedstocks, and coal gasification all produce dilute hydrogen. Dilute hydrogen is also often available as a by-product in various chemical industries. To obtain pure hydrogen, small-scale users generally use expensive electrolysis methods or purchase hydrogen from commercial vendors. On the other hand, large scale users use state of the art purification techniques such as scrubbing, cold separation, pressure swing adsorption or membrane diffusion separators. In conventional electrolytic type processes, the hydrogen contained in the water is converted to gaseous hydrogen by oxidizing the water in an electrochemical cell. In other electrolytic methods, hydrogen contained in a gaseous mixture is converted to ionic form in contact with a palladium membrane. The ionic hydrogen at the surface of the membrane is converted to atomic hydrogen and the atomic hydrogen then passes through the membrane.
At the output end, atomic hydrogen is converted to molecular hydrogen and pure hydrogen is thereby produced. However, the above method is disadvantageous in that it is sensitive to temperature and impurities such as sulfur and hydrocarbon compounds. Also, the hydrogen pressure on the input side of the membrane must always be higher than the pressure on the output side. Palladium-based membranes are also susceptible to loss of stability after repeated cycles of adsorption and desorption. US Pat. No. 3,446,674 discloses an electrochemical converter that similarly relies on atomic hydrogen being generated and passed through a palladium membrane.
More specifically, the US patent discloses a converter that uses an anode equipped with a dehydrogenation catalyst. The cathode member is a palladium membrane that is permeable to hydrogen. An electrolyte is placed between the anode and cathode and a power supply is connected to the anode and cathode to complete the circuit. In operation of this converter, a gaseous mixture such as hydrocarbons and water vapor is passed into contact with the anode and undergoes a reaction under the influence of a dehydrogenation catalyst and electric current to produce hydrogen ions and carbon dioxide. Hydrogen ions pass from the catalyst through the electrolyte to the cathode palladium membrane, where they receive electrons and form atomic hydrogen. The atomic hydrogen then permeates through the membrane and is formed into substantially pure molecular hydrogen at the manifold on the exit side of the membrane. The above US patent also discloses that the anode of the converter of the invention can be formed by coating a conductive metal screen with a suitable dehydrogenation catalyst and treating the screen with a hydrophobic material. In this regard, the above-mentioned U.S. patent discloses that other structures containing metallic elements that are inherently permeable to gas may be used to create the anode, such as the porous electrode structure disclosed in U.S. Pat. No. 2,928,783. and that the metals are catalytic in nature, such as palladium and platinum. The converter described in US Pat. No. 3,446,674 relies on the permeation of atomic hydrogen through a palladium cathode membrane to effect hydrogen purification. This makes the electrolyzer sensitive to temperature changes and impurity levels and requires large pressure differentials across the palladium for operation. Additionally, the above patent recognizes that a portion of the hydrogen will be generated on the cathode side of the palladium membrane. This will result in hydrogen loss and seal leakage. Also, palladium membranes have a high hydrogen overvoltage which tends to result in high power consumption. Finally, the stability of the membrane in acid media and under the required operating temperatures and repeated cycling is also questionable. The converter of the above patent is therefore disadvantageous in a number of respects. It is therefore an object of the present invention to provide a device and a method for purifying hydrogen which does not suffer from the above-mentioned disadvantages. Another object of the present invention is to provide a hydrogen purification system and method capable of providing an output gas pressure approximately equal to or greater than the input gas pressure. Yet another object of the present invention is to provide a hydrogen purification system and method that is highly stable and provides increased output capacity. SUMMARY OF THE INVENTION In accordance with the principles of the present invention, the present invention provides an anode gas diffusion electrode, a cathode diffusion electrode, a first channel adjacent the anode electrode, a second channel adjacent the cathode electrode, and a sandwich channel between the electrodes. This is accomplished by the use of a hydrogen purification device that includes an assembly that includes an acid electrolyte and a device for supplying a voltage across the electrodes. As used herein, the term "gas diffusion electrode" means an electrode that has macroscopic pores sufficient to allow the passage of molecular hydrogen. Electrodes meeting this requirement have pores approximately equal to or larger than 1 micron. Using the above configuration for a purification device, the impure or dilute hydrogen supplied to the first channel of the assembly is converted to molecular hydrogen via the anode gas diffusion electrode, the electrolyte and the cathode gas diffusion electrode, and this hydrogen is transferred to the cathode gas diffusion electrode. It passes through the electrode and enters the second channel as substantially pure hydrogen. Because hydrogen passes through the cathode electrode in molecular form, the disadvantages associated with passing in atomic form experienced by the converter of US Pat. No. 3,446,674 are substantially eliminated. Furthermore, the device exhibits good stability since the gas diffusion electrode is highly stable in acid electrolytes. In another aspect of the invention, the plurality of assemblies are arranged in a stack and a common input manifold supplies impure hydrogen to all first channels and a common first output manifold supplies impure hydrogen to all first channels. Substantially pure hydrogen is extracted from two channels. In this case, the first channel feeds a second common output manifold that receives the gas remaining after hydrogen removal. In yet another aspect of the invention, pure hydrogen is removed at increased pressure by including the stack within the pressure vessel. BRIEF DESCRIPTION OF THE DRAWINGS These and other features and aspects of the invention will become more apparent from the following detailed description read in conjunction with the accompanying drawings. FIG. 1 depicts in cross-section an apparatus for purifying hydrogen in accordance with the principles of the present invention. FIG. 2 illustrates a partially cut-away view of an assembly useful for the apparatus of FIG. FIG. 3 illustrates the assembly of FIG. 2 arranged in a similar assembly to form a stack. FIG. 4 shows the stack of FIG. 3 placed in a pressure vessel. FIG. 5 illustrates a series arrangement of devices similar to that of FIG. FIG. 6 shows typical current-voltage characteristics of the device of FIG. FIG. 7 shows the relationship between the voltage applied to the apparatus of FIG. 1 and the fraction of hydrogen converted to pure hydrogen. The present invention will be explained below based on the drawings. FIG. 1 shows an apparatus 10 including an assembly 1 for purifying hydrogen gas in accordance with the principles of the present invention. The assembly 1 includes spaced apart gas diffusion anode electrodes 2 and gas diffusion cathode electrodes 3 with a zone or space therebetween for receiving an electrolyte 4 . The second plate 7 is adjacent to the cathode electrode 3 and forms a second set of channels 7a for receiving the hydrogen purified by the assembly 1.
The first plate 5 is adjacent to the anode electrode 2 and forms a first set of channels 5a for introducing impure hydrogen flow and feed into the assembly 1. The device 1 is a DC source shown as a source 11 providing a voltage across an anode electrode 2 and a cathode electrode 3.
Contains voltage source. Lead wire 18 connects the positive terminal of source 11 to the anode electrode and lead wire 19 connects the negative terminal of the source to cathode electrode 3. The electrolyte 4 between the electrodes 2 and 3 can be an acid electrolyte contained within a microporous separator or membrane, but may also be received directly in the zone or space without a separator or membrane. The acid electrolyte is preferably phosphoric acid because of its stability at high temperatures, although sulfuric acid can be used, for example. The separator that holds the acid electrolyte must be formed from an electrical insulator that is stable in the operating environment. Silicon carbide mixed with Teflon as a binder has been found to be stable for use in hot phosphoric acid and is a preferred material. The electrolyte 4 can also be provided by a solid polymer type electrolyte, such as a solid polymer hydrogen ion exchange membrane. According to the invention, the anode electrode 2 and the cathode electrode 3 are formed as gas diffusion electrodes with a catalytically active surface. Such electrodes generally include a porous conductive layer or substrate, such as porous carbon, contacted with a small amount of a metal catalyst, such as metallic platinum. Typically the electrode should have a porosity of 50-90 percent and a metal catalyst content of 0.05-0.5 mg/ ^cm2 . The assembly 1 separates hydrogen from other gases in the stream and supplies it to the second channel group 7a by selective electrochemical action.
provides purification of an impure or dilute hydrogen stream fed to a. This selective electrochemical action is based on a highly reversible hydrogen oxidation-reduction reaction. In particular, the following equations and equations govern the reactions at the anode and cathode electrodes, respectively. Anode H ₂ (g)...>2H ⁺ +2e ^- [] Cathode 2H ⁺ +2e ^- ...>H ₂ (g) [] More specifically, at the anode electrode, hydrogen in the impurity stream diffuses through the electrode and A metal catalyst is contacted which is partially wetted by an acid electrolyte. The three-phase interface required for the hydrogen oxidation reaction (conversion of molecular hydrogen into hydrogen ions) is thereby established. This reaction takes place in the presence of an applied electric current and hydrogen is ionized and absorbed into the electrolyte according to the equation. The hydrogen ions in the solution are then transported to the cathode electrode 3 under the influence of an applied electric field. At the cathode surface, hydrogen ions are reduced by electrons supplied from an external circuit according to an equation to produce molecular hydrogen. This molecular hydrogen then diffuses into the pores of the cathode and enters the second
It enters channel group 7a. The only small electrical potential required is provided by source 11 due to the hydrogen redox reactions occurring at a substantial rate. Assembly 1 is highly selective for hydrogen transfer since diluent or impurity gases normally present in impure hydrogen streams cannot undergo redox reactions at such low applied potentials. The resulting molecular hydrogen produced at the cathode electrode 3 and supplied to the second channel group 7a is therefore hydrogen of very high purity. It should be noted that the amount of electrical energy consumed in the assembly 1 to produce a given amount of purified hydrogen depends to a large extent on the electrical resistance exhibited by the assembly. This fact favors the use of thin large area components for assembly. For this purpose, FIG. 2 shows an assembly 1 formed from grooved contact plates as plates 5 and 7. These plates support thin porous anode electrodes 2 and cathode electrodes 3 between which a thin porous membrane 4' filled with electrolyte is sandwiched. In the case shown in FIG. 2, the first channel group 5a in the first plate 5 consists of a first channel 5a' which is open at its input and output ends. The open input ends of the channels receive impure hydrogen gas and the open output ends receive the impure gas and the second channel group 7a.
Evacuate all hydrogen not transferred to the tank. Second
Channel group 7a consists of a second channel 7a' which is transverse to channel 5a'. Channel 7a' is closed at one end and assembly 1
are open at their opposite ends for the supply of pure hydrogen from the As can be seen and shown in FIGS. 2 and 3, plates 5 and 7, electrodes 2 and 3
The electrolyte membrane 4' can then be repeated to form a stack 31 of assemblies. In this case, so that the release input and release output ends of those first channels are lined up, respectively,
Also, stack the released output ends of these second channels side by side. In the case shown, a single plate serves as plate 5 of one assembly and plate 7 of the next successive assembly via a transverse set of channels 5a' and 7a' on its upper and lower surfaces. A first input manifold 32, common in a stack of such assemblies, receives impure hydrogen from an inlet port 33 and supplies it to the input end of the channel 5a' of the assembly. The purified hydrogen exits the assembly via the open end of channel 7a' and exits port 3.
5 into a common first output manifold 34. A second common output manifold 36 receives impure and untransferred hydrogen and these gases exit the manifold via its outlet port 37. In the stack shown in FIG. 3, the assembly 1 is compressed between top and bottom flat compression plates 38 and 39. Plates 38 and 39 are secured by cross members 41, 42 which are held together by bolts 43 and securing rods 44. The cross members are supported by pads 45 on plates 38 and 39. terminals 46 and 47
(not shown) allows application of a voltage source potential across the stack assembly. In another aspect of the invention, the purified hydrogen gas provided by assembly 1 may be pressurized at a higher pressure than the pressure of the impure hydrogen feed stream. This can be accomplished by placing the assembly in a pressure vessel and collecting pure hydrogen gas at higher pressure. FIG. 4 shows the bell-shaped end section 51 connected to the main body section 54 by screw nails 53.
and 52 shows the stack of FIG. 3 placed in such a pressure vessel formed from. section 5
Openings 55 and 56 in 4 allow passage of ports 33 and 37 of manifolds 32 and 36 of stack 31. The stacked manifold 34 as shown in FIG. 3 is removed and the purified hydrogen is allowed to enter and be collected directly inside the vessel. A pressure regulator 61 is located at the outlet port 57 of the container. Regulator 61 controls the pressure of the purified hydrogen leaving the vessel and can be adjusted to the desired pressure for the purified gas. The pressure at which the purified gas can be raised depends on the capacity of the electrolyte in each of the assemblies 1 to be maintained between the electrodes of the assemblies. If even higher pressures are desired, solid polymer electrolytes should be used. However, if a liquid electrolyte such as sulfuric or phosphoric acid is to be used, the silicon carbide membrane described above augmented with a layer of ultrafine carbon particles can be used. In this case, the ultrafine carbon layer provides a membrane structure with very small pore diameters and as a result the structure provides strong retention of the electrolyte due to capillary forces. Using the present invention, purified hydrogen can be produced at pressures higher than the pressure of the impure feed stream alone at the expense of energy required for reversible compression of hydrogen. The amount of energy required for the reversible separation of n x 0.45359 kg moles (n pound moles) of hydrogen at temperature T is given by the formula W = (2.3RT) nlog ₁₀ (P ₂ /P ₁ ) [] (where P ₂ is the feed pressure, P ₁ is the feed pressure and R is the gas constant). The reversible work to separate hydrogen from a feed gas containing 20% hydrogen at a temperature of 150 °C can be calculated from the equation and for impure and purified hydrogen pressures of 1 and 20 atm. Provided below.

【table】

[Table] Using the above table, the energy required for reversible compression of hydrogen gas at 1 to 20 atmospheres is 9.987×
It was determined to be 10 ³ Btu/1 Kg-mol (4.53×10 ³ Btu/lb mole). Thus with assembly 1 only that much energy would be required to provide purified gas at 20 atmospheres rather than 1 atmosphere. Note that multiple assemblies similar to assembly 1 can be placed in series to produce ultra-pure hydrogen products. FIG. 5 illustrates a preferred tandem arrangement of assemblies in series in which the first assembly 61 uses phosphoric acid as the electrolyte and the second assembly 62 uses a solid polymer electrolyte. In this case, a first output manifold of the first assembly can be coupled to a first input manifold of the second assembly. With this arrangement, most undesirable impurities in the hydrogen stream, including carbon monoxide, are removed from the first assembly 61.
removed or separated from the hydrogen in it. A second assembly 62 operating on an essentially carbon monoxide-free stream can then provide ultra-pure hydrogen gas at elevated pressures. The energy requirements for operating the assembly 1 of FIG. 1 are determined by the irreversible losses resulting from the electrical and contact resistances of the plates 5 and 7, the electrodes 2 and 3, and the electrolyte membrane. These energy losses appear as heat in the assembly and serve to increase its operating temperature. The latter temperature depends on the impure feed gas temperature used and the current density. Typically, when phosphoric acid is used as the electrolyte, it is preferred to operate the assembly at a temperature in the range of 100-250°C. By operating at current densities in the range from 200 to 600 Ma/ ^cm2 , the above operating temperature range can be obtained without the use of separate heating and/or cooling devices. Diluents or impurities in the impure hydrogen feed stream diffuse in their normal gaseous state through the anode, electrolyte membrane and cathode electrodes of assembly 1 at a low but limited rate. Diffusion of undesirable impurities can be reduced by increasing the thickness of the electrolyte membrane and collecting hydrogen gas at higher pressures. However, increasing the thickness of the membrane increases its electrical resistance and thereby increases the energy requirements to operate the assembly. Therefore, increasing purity in this manner must be considered against all attendant increased energy requirements. As is known, carbon monoxide is one of the common impurities found in conventionally produced dilute hydrogen. If platinum is used as a catalyst for electrodes 2 and 3, carbon monoxide can render the platinum catalyst ineffective by absorption onto the active metal sites if the electrode temperature is too low. Therefore, if there is an appreciable concentration of carbon monoxide in the gas to be purified by assembly 1,
By maintaining the operating temperature of the electrolyzer above 190°C all significant catalyst poisoning effects can be eliminated. Figure 6 shows assembly 1 of Figure 2 using an electrolyte membrane having an area of 25 cm ² (0.027 square feet).
shows the current-voltage characteristics of Its characteristics are for two different impure hydrogen feed stream compositions. These characteristics indicate that higher cell potentials need to be applied with lower hydrogen feed concentrations to overcome condensation effects and diffusion losses. The effect of the fraction of hydrogen removed from the impure feed stream on the potential required to be applied to the assembly 1 is shown graphically in FIG. As can be seen, the potential remains essentially constant until more than 90% of the hydrogen in the feed stream is removed. Because of the high migration rate of the hydrogen ions compared to the gradual and slow diffusion of gaseous undesirable components in the assembly 1, a high degree of separation occurs even in a single stage device. Table 1 below provides gas chromatography results for the impure feed gas and purified gas of the apparatus of FIG.

Table 1 above shows the results of product hydrogen analysis by gas chromatography obtained in a 25 cm ² single cell operated at 600 Ma/cm ² . In all cases, the above arrangements are merely illustrative of the many possible specific embodiments representing applications of the invention. Many and modified other arrangements can be readily devised in accordance with the principles of the invention without departing from the spirit and scope of the invention.

[Brief explanation of the drawing]

FIG. 1 depicts in cross-section an apparatus for purifying hydrogen in accordance with the principles of the present invention. FIG. 2 illustrates a partially cut-away view of an assembly useful for the apparatus of FIG. FIG. 3 illustrates the assembly of FIG. 2 arranged in a similar assembly to form a stack. FIG. 4 shows the stack of FIG. 3 placed in a pressure vessel. FIG. 5 illustrates a series arrangement of devices similar to that of FIG. 6th
The figure represents typical current-voltage characteristics of the device of FIG. FIG. 7 shows the relationship between the voltage applied to the apparatus of FIG. 1 and the fraction of hydrogen converted to pure hydrogen. DESCRIPTION OF SYMBOLS 1... Assembly, 2... Anode electrode, 3... Cathode electrode, 4... Electrolyte, 5... First plate, 5
a'...first channel, 7...second plate, 7a'...second channel, 10...device of the present invention, 11...DC voltage source, 18...lead wire, 19...lead wire, 31...
Stacking of assemblies, 32...first input manifold, 33...inlet port, 34...first output manifold, 35...outlet port, 36...second output manifold, 37...outlet port,
38... Compression plate, 39... Compression plate, 41
...cross member, 42...cross member, 43...bolt, 44...fixing rod, 45...pad, 46...terminal,
51... Bell shaped end section, 52... Bell shaped end section, 53... Screw nail, 54... Main body section, 55... Opening, 56... Opening, 57... Outlet port, 61 (Figure 4)... Pressure regulator, 61 (5th
Figure)...first assembly, 62...second assembly.

Claims (1)

Claims: Each of the plurality of assemblies includes: 1 a gas diffusion anode electrode, a first plate adjacent to the electrode, a gas diffusion cathode electrode, and a second plate adjacent to the electrode; a first channel for conveying a hydrogen-containing medium to an anode electrode, each of the first channels having a release input and an output end, and the second plate having a second channel, each of the first channels having a release output. the anode and cathode electrodes are spaced apart to form a zone for receiving electrolyte therebetween, and the assembly is configured to align the release input and release output ends of their first channels, respectively; arranged in a stack with the release output ends of the second channels side by side, and further provided with means for applying a voltage to the anode and cathode electrodes of each of said assemblies to direct said hydrogen-containing medium to the input ends of said first channel. a common first input manifold at the input end of the first channel for conveying; and a common first input manifold for receiving the hydrogen content of increased purity from the output end of the second channel.
a first output manifold common to the output ends of the channels; and a first output manifold common to the output ends of the first channels for receiving gas exhausted from the first channels from the output ends of the first channels. 2
A hydrogen purification device characterized by being equipped with an output manifold. 2. The apparatus of claim 1, wherein the end of the second channel opposite the released output end is closed. 3. the first channels of the plurality of assemblies all extend in a direction substantially parallel to the first direction;
2. The apparatus of claim 1, wherein the second channels all extend in a direction substantially parallel to a second direction, the second direction being transverse to the first direction. 4. The apparatus of claim 1, wherein the gas diffusion anode and cathode electrodes include a metal catalyst. 5. The device according to claim 4, wherein the catalyst is platinum. 6. The device of claim 1, wherein the electrolyte is an acid electrolyte. 7. The device of claim 6, wherein the acid is phosphoric acid. 8. The device of claim 1, including a microporous membrane located in the zone between the electrodes, said membrane containing said electrolyte. 9. The device of claim 1, wherein the electrolyte is a solid polymer electrolyte. 10. The apparatus of claim 1, including a container for receiving hydrogen in said second channel. 11. The apparatus of claim 10, further comprising a pressure regulator for maintaining the pressure of hydrogen in the container at a predetermined pressure. 12. The apparatus of claim 11, wherein the predetermined pressure is approximately equal to or greater than the pressure of the hydrogen-containing medium. 13 having another plurality of assemblies separately arranged to align the release input and release output ends of their first channels and to align the release output ends of their second channels, respectively; further apparatus is provided for applying a voltage to the anode and cathode electrodes of each of the plurality of further assemblies arranged in a stack; a separate first input manifold common to the input ends of said second channels for receiving hydrogen content of increased purity from the output ends of said second channels of said separate assembly; a first output manifold common to the output end of the first channel for receiving gas exhausted from the first channel from the output end of the first channel of the other assembly; 2. The apparatus of claim 1, further comprising a second output manifold and a means for connecting the first output manifold to the first input manifold. 14 Each of the first assemblies includes a microporous membrane disposed between an anode and a cathode electrode and phosphoric acid contained in the membrane, and each of the second assemblies includes a solid polymer electrolyte disposed between the anode and cathode. 14. The device according to claim 13, comprising as an electrolyte. 15 Each assembly includes one or more gas diffusion anode electrodes, an adjacent first channel, a gas diffusion cathode electrode, an adjacent second channel, and an electrolyte disposed between the anode and cathode electrodes. a method for purifying hydrogen utilizing a first channel of the one or more assemblies, comprising: supplying a hydrogen-containing medium to a first channel of the one or more assemblies; and applying a voltage between the anode and cathode gas diffusion electrodes, thereby or the hydrogen content in the medium in the first channel of the one or more assemblies is passed through the anode electrode, the electrolyte and the cathode electrode of the one or more assemblies with increased purity to the first channel of the one or more assemblies. 2 channels, and removing the hydrogen from the second channel of the one or more assemblies at a pressure greater than the pressure of the medium.